Im not sure if some is bug and other parts on but here is somethings ive noticed recently about vlads sanguine pool in the last 2 games.
-When you go over cass's pool of poisen that you can place on the ground while in sanguine pool, you pick up the DoT and poisen damage that it places on champions that walk over it
-Ezreal's q hit me a couple times during the game, i counter 3 in the short time i noticed it
-Iceborn Gauntlets slow is placed on vlad while he is in sanguine pool and on top of the iceborn gauntlet aoe